The System 7.5 installation disks The System 7.5 installation disks (800K version) allow you to upgrade the system software on your Macintosh II, Macintosh Plus, or Macintosh SE computer to version 7.5 using 800K floppy disks. If your Macintosh II, Plus, or SE does not have a 1.4 MB floppy disk drive, you can use the 800K installation disks—along with the System 7.5 Upgrade Kit— to upgrade to System 7.5. The 800K disks do not provide the software for installing QuickDraw GX or PowerTalk.